Phosphazenes are compounds that contain --P=N-- bonds and have a general formula [NPR'R"].sub.n, wherein n is .gtoreq.3. Such compounds have thousands of derivatives along with a change in R' and R". In addition to a variation in R' and R", the structures of the phosphazenes can be classified into cyclic compounds and linear compounds. When n=3, the compounds become benzene-like hexagonal planar compounds. When n=4, the compounds become octangular cyclic compounds. Among the identified cyclic phosphazenes, the maximum n value is 10. Phosphazenes with n.gtoreq.3 can also exist in a linear form. Phosphazenes have always been viewed as a potential flame retardant in view of a synergistic effect of P and N elements. When R' or R" is a group containing an active hydrogen (such as amino or hydroxyl), such phosphazenes can even be used to cure a resin having functional group(s) that can react with an active site, such as polyurethane having isocyanate terminals and epoxy resins. A typical example of the amino-containing phosphazene that can be used as a curing agent and a flame retardant for the polyurethane and epoxy resins, has a structure of N.sub.n p.sub.n (NH.sub.2).sub.x (OR).sub.2n-x, wherein 1.ltoreq.x&lt;2n, and R is phenyl or C3-C6 alkyl. The conventional processes for preparing such amino-containing phosphazenes basically can be classified into two types. The first type of preparation process comprises amination and then esterification; and the second type of preparation process comprises esterification and then amination. The following Scheme 1 shows an example of the first type, in which N.sub.3 P.sub.3 (NH.sub.2).sub.2 (OC.sub.3 H.sub.7).sub.4 is synthesized: ##STR1## ##STR2##
In Scheme 2, the amination step can only be completed under a pressurized state, which increases the complexity and the safety concerns of the process.
The above-mentioned processes all have a defect of having too many operational steps thereof. Take Scheme 1 as an example:
Step 1: amination; PA0 step 2: separating the organic phase from the aqusous phase after the amination; PA0 step 3: removing the organic solvent by evaporation, thereby obtaining N.sub.3 P.sub.3 (NH.sub.2).sub.2 Cl.sub.4 ; PA0 step 4: reacting the intermediate product N.sub.3 P.sub.3 (NH.sub.2).sub.2 Cl.sub.4 with NaOC.sub.3 H.sub.7 under refluxing; PA0 Step 5: after reaction, washing off NaCl with water; and separating the organic phase from the aqueous phase; PA0 Step 6: drying off residual moisture in the organic phase; and PA0 Step 7: removing the organic solvent from the organic phase by evaporation, thereby obtaining the product.